For example, in Japan, with diversification and westernization of eating habits in recent years, consumption of rice tends to decrease every year. Therefore, development of rice-based processed foods is strongly required in order to increase consumption of rice, and there have been provided dried cooked rice for instant food products (rice porridge, rice porridge with other ingredients, risotto, and the like) (Patent Literature 1), and frozen foods (Patent Literature 2).
It is strongly required to enhance the reconstitutability of dried cooked rice particularly used for instant food products, and for example, methods for processing gelatinized rice or puffed dried rice used for instant food products and utilizing it have been studied and developed in order to shorten reconstitution time for dried cooked rice or to improve the reconstitutability (Patent Literature 3 to 5). Here, gelatinized rice refers to rice obtained by cooking polished white rice while preventing its tissue from being broken, and then quickly drying the cooked rice so that it has a moisture content of 17% or less while keeping gelatinized state of starch. Thereby, starch can be preserved for a long time while keeping its gelatinized state, and such gelatinized rice can be reconstituted usually within several tens of minutes into a similar state as cooked rice only by adding water or boiling water. Puffed dried rice refers to dried rice obtained by gelatinizing (cooking) rice, adjusting its moisture content, and then drying the resulting rice at high drying temperature to puff its tissue. Such puffed dried rice is reconstituted for eat by adding boiling water and allowing to stand for a few minutes, or reconstituted for eat by adding water and cooking in a microwave.
Dried cooked rice generally used is produced by drying with hot air or vacuum-freeze-drying cooked rice obtained by a usual method for cooking rice. In the production process, it is required to mechanize the steps of, for example, loosening, weighing, filling, and forming cooked rice, and in these steps, improvements of cooked rice such as reduction in sticking of grains of rice of each other and adhering of grains of rice to a machine are required.
Stickiness and hardness of cooked rice are very important factors for its eating quality. White cooked rice and most processed cooked rice tend to be easy to be loosened but become cooked rice having a hard texture without stickiness when the moisture content after cooking rice is low. On the other hand, when moisture content after cooking rice is high, cooked rice having moderate stickiness and hardness can be obtained but the cooked rice tends to be difficult to be loosened to cause uneven drying and unevenness of texture. Therefore, it is desired to develop a method for producing processed cooked rice that can cope with both easiness of cooked rice to be loosened and improvement in texture in cases where the moisture content after cooking rice is high.
There has been a case where an enzyme composition for cooking rice comprising a heat-resistant α-amylase was developed for the purpose of improving easiness of cooked rice to be loosened (Patent Literature 6). However, its effect is not necessarily satisfactory, and a more effective method is required.